Bug with alternateOf method in patent call

[madgpap]

For example, for this patent:
https://beta.openphacts.org/2.1/patent?uri=http%3A%2F%2Frdf.ebi.ac.uk%2Fresource%2Fsurechembl%2Fpatent%2FUS-8951580-B2&app_id=b8321556&app_key=ef7d821ffba6fa85a722f95f889ce761

This returns hundreds of alternateOf (=same patent family) patents which is not true (see https://www.surechembl.org/document/US-8951580-B2). Why is this?
Because some patents have a dummy family ID value of -1. The grouping of patents by family ID should ignore these dummy values of -1. As it stands now, these are all spuriously grouped together as 'alternateOf'.